Universal Serial Bus (USB) provides an interface standard for communication between a host and external devices. USB has enjoyed success in the marketplace due to the relatively small form factor of its connectors and its relatively high data throughput rates (particularly for USB v.2.0). Further, USB is highly user-friendly, allowing for plug-and-play connections and hot-swapping capability (i.e., allowing the USB device to be plugged into and removed from a host without requiring the host to be rebooted).
As discussed herein, a USB host typically has a USB socket for coupling with an electronic device (i.e., a USB device) having a corresponding USB plug. Hosts may include, but are not limited to desktop units, laptop units, personal digital assistants (PDAs), game consoles, electronic entertainment devices, and hubs. USB devices may include, but are not limited to keyboards, mice, displays, printers, scanners, camera, electronic entertainment devices such as digital audio devices, removable drives, etc.
An external device with USB capability has at least one USB plug. Generally, the USB plug is configured to mate with the host via a host-side USB socket (i.e., receptacle) using friction force. To facilitate discussion, FIG. 1 shows an example of a USB plug and socket. On a USB plug 100, a rectangular metal housing 102 has holes 104 located on the wide side of metal housing 102. Located inside metal housing 102 are plug pins 106, which reside a surface of substrate 108 (i.e., the downward-facing surface due to the orientation of the USB plug in FIG. 1).
On a USB socket 110, receptacle shell 112 has leaf springs 114 located on the wide side of a rectangular receptacle shell 112. At the end of each leaf spring 114 is a tip 116, which is designed to engage with a hole 104 when plug 100 is fully inserted into socket 110. The contact point may also be elsewhere, such as on a bend on the leaf spring. Inside receptacle shell 112 are socket pins 118 residing on a substrate 120. Socket pins 118 are configured to mate with plug pins 106 when USB plug 100 is inserted into USB socket 110.
Friction force allows USB plug 100 to stay mated with USB socket 110. Friction force is created when socket pins 118 make contact with plug pins 106. Friction force is also produced when leaf springs 114 slides along metal housing 102. Yet another source of friction force occurs when tips 116 are lodged inside holes 104.
A USB plug may be protected from environmental damage by capping it with a USB cap. A USB cap may be made of plastic or rubber or a similarly suitable material, typically without a metallic receptacle shell. The USB cap generally relies on friction to keep the cap engaged with the USB plug tip.
It has been found that friction force alone is insufficient in keeping some USB devices connected to their USB hosts or USB caps. If the USB device is not securely connected to the USB host, the USB device may be easily disconnected unintentionally, e.g., when the USB host and USB device combination is accidentally bumped. If the USB device is intended to be a portable device, the USB device may be inadvertently separated from its USB cap or from its USB host when subjected to movement, for example. In either of the above examples, the result is an unintended and undesirable separation and/or possible loss and/or damage to the USB host, the USB device, or both.